The present invention relates to a terminal unit, and more particularly relates to a one-touch operating terminal unit having a push button which may be lightly pushed to easily and fixedly hold an electrically conductive wire of a single thick line or a wire of a plurality of bundled or twisted thinner lines which may be loosened to swell by utilizing a compression spring in connection with the push button so as to be compressed with a principal of lever to produce a large stroke of operation with application of a light operating force thereto.
So far there have been proposed many terminal units having a one-touch push button which is operated to hold the electrically conductive wire. Such terminal units are generally provided with a plate spring only or a plate spring and a compression spring arranged in combination in connection with the push button.
In case of the terminal unit provided with the plate spring only, the plate spring has a hard spring property to hold the electrically conductive wire with a strong force. However the hard spring property (a large spring constant) will progressively require a stronger force as the push button is pressed down. In other words, the plate spring may be pressed at first with a stroke which is caused by relatively weak force applied to the push button, but will be abruptly heavy during the stroke of operation. In order to press the plate spring to the end of stroke, a maximum force of about 21.6N (2.2 kgf) is required.
The terminal unit is manually operated to hold the electrically conductive wire. Since the push button is so small, the finger top or finger nail will be subjected to a heavy load which will give a considerable pain to the finger top or finger nail when pushing down the push button to connect the electrically conductive wire to the terminal unit.
Thus the finger top or finger nail is required to apply a considerably strong force to the push button until the plate spring is pressed down to allow the electrically conductive wire to be inserted. This will often cause the terminal unit to fail to correctly hold such a wire of a plurality of bundled or twisted wires which may loosen apart from each other. It is, therefore, required to provide a terminal unit for the electrically conductive wire of single thick line and another terminal unit for the wire of a plurality of bundled or twisted thinner lines.
Even in case of the terminal unit provided with a plate spring and a compression coil spring in combination, the moving direction of the push button is not in alignment with the compressing direction of the compression coil spring, causing it difficult to produce a required light and large stroke of operation when the push button is pushed. Further the terminal unit fails to have the plate spring and the compression coil spring arranged in a stabilized engagement with each other. These two parts are, therefore, displaced from each other during the stroke thereof due to pushing operation of the push button, causing the pushing operation to be unsmooth and causing the wire holding force to be unstabilized.